Squats, lunges, plyometric jump training. Do them properly, google for form and good practice. My tip if you lack weights etc. would be 21’s. Deliciously simple, horrifically painful but great results. Here’s how it works:
Start with 21 press-ups
Then jump to your feet in one motion.
Do one body weight squat, keep your knees over your toes, sit backwards and drive all the way up.
Then do 20 press-ups.
One squat.
19 Press-ups
One Squat
18 Press ups……
continue all the way down to 1 press-up, 1 squat. By the end your press-ups will be desperate!
Then start with 1 squat 1 press-up
2 Squats 1 press-up
3 squats 1 press-up
4 squats 1 press-up
all the way back up till you are on 21 body weight squats 1 press-up.
In the end you will have done over 250 of each, and if you have done it correctly you won’t be able to walk in the morning the first time! But do it once a week for a few weeks and you will improve your neuromuscular facilitation (strength in a muscle at a given size) no end and will feel strong to the end of even long descents.
The first time I did this was with half the Sale Sharks Rugby Union squad, I had to crawl to the shower the following day but I earned respect and my leg strength improved so fast.
Good luck,
Richard
Pedal Precision: Professional Bike Fit and Cycling Injury Specialists
http://www.pedalprecision.com